Physicochemical properties of starch nanocomposite films enhanced by self-assembled potato starch nanoparticles
Introduction
In recent years, because of grievous resource shortages and environmental pollution, a great number of research studies have focused on obtaining environmentally friendly material in order to solve the problems created by plastic waste (Yasser, 2013). The use of natural polymers is promising for solving resource shortages and minimizing the environmental problems compared with conventional plastics. Some works have studied the possibility of substituting the plastics with natural polysaccharide raw materials with similar properties.
Starch, as a natural, renewable, and biodegradable biopolymer, has been evaluated in its film-forming ability for applications in food packaging (Jiménez, Fabra, Talens, & Chiralt, 2012). It is capable to form a continuous matrix and has low permeability to oxygen (Campos et al., 2011, Dole et al., 2004), lower cost compared to other non-starch films. Films based on starch are transparent (Jiménez et al., 2012, Mali et al., 2004), odorless, tasteless, and colorless. However, when compared to other plastic polymers, films based on starch exhibit several drawbacks, such as their hydrophilic character and poor mechanical property. These problems could be addressed by adding organic or inorganic nanofillers to the starch matrix (Xie, Pollet, Halley, & Averous, 2013). In recent years, the addition of starch nanoparticles (SNPs) to starch matrix to improve the properties of films has aroused the interest of many researchers (Dai et al., 2015, García et al., 2011, Jiménez et al., 2012). The unique characteristics—such as biodegradability, impressive mechanical properties, low permeability, and the same chemical structures as the starch matrix—make SNPs an ideal candidate as reinforcement for the fabrication of starch–based nanocomposite films (Lin, Huang, & Dufresne, 2012). In this way, starch films can improve mechanical and barrier properties and act as bioactive packaging. Studies have shown that the tensile strength (TS), Young modulus, and elongation at break (Eb) of the nanocomposite containing starch nanocrystals were improved (Kristo and Biliaderis, 2007, Li et al., 2015). Shi, Wang, Li, and Adhikari (2013) also demonstrated that added SNPs in starch films led to lower water vapor permeability than that of control film.
Potato starch is one of the main commercial starches widely used for sizing paper and textiles and for stiffening laundered fabrics. Potato starch nanocrystals are traditionally prepared by mechanical treatment (Szymońska, Targosz-Korecka, & Krok, 2009) and acid hydrolysis and could serve as an effective reinforcing agent for natural rubber nanocomposites (Rajisha, Maria, Pothan, Ahmad and Thomas, 2014). Most recently, Sun, Li, Dai, Ji, and Xiong (2014a) proposed a time saving regeneration method that combines enzymolysis with recrystallization to prepare SNPs. Corre and Angellier-Coussy (2014) have stated that this is the most innovative approach proposed in the last years. To our knowledge, nanocomposites impregnated with different levels of potato SNPs fabricated by self-assembly have not yet been reported. Therefore, in this study, potato SNPs were prepared by self-assembly of short amylose debranched from potato starch. The influences of potato SNPs on the physicochemical properties of pea starch-based composite films were evaluated. This will provide the theoretical basis to produce biodegradable starch films that have better mechanical strength, barrier properties, and thermal stability.
Section snippets
Materials
Pea starch (about 40% amylose) and potato starch (about 31% amylose) were obtained from Tianjin Tingfung Starch Development Co., Ltd (Tianjin, China). Pullulanase (E.C.3.2.1.41, 6000 ASPU/g, 1.15 g/mL) (ASPU is defined as the amount of enzyme that liberates 1.0 mg of glucose from starch in 1 min at a pH of 4.4 and 60 °C) was obtained from Novozymes Investment Co. Ltd. (Beijing, China). All other reagents used were of analytical grade.
Preparation of potato starch nanoparticles (SNPs)
Potato SNPs were prepared using the method described by Sun
Scanning electron microscopy of potato starch nanoparticles
Potato SNPs observed under a SEM are shown in Fig. 1. Potato starch granules had smooth surfaces and oval shapes (Fig. 1A), whereas SNPs were observed to be spherical in shape with particle sizes primarily within the range of 15–30 nm (Fig. 1B–D). The SNPs prepared employing 7.5% (w/v) starch suspension had large particles that were about 50–120 nm in size, and only a few small particles below 50 nm were observed. This may be attributed to agglomeration of particles due to strong hydrogen
Conclusion
In this work, potato SNPs was fabricated through self-assembly of short amylose. SEM micrographs revealed that the nanoparticles had globular shapes with diameters ranging from 15 to 30 nm. With the addition of different levels of SNPs, physicochemical properties of pea starch-based nanocomposite films were enhanced. SNPs addition to films increased TS and decreased Eb compared to control film. WVP was reduced with SNPs incorporation. DSC results demonstrated that incorporation of SNPs
Acknowledgments
The authors thankful for the financial support the Qingdao Municipal Science and Technology Plan Project (14-2-3-48-nsh).
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